Palladium is widely used in the manufacture of electrically conductive thick films for microelectronic devices. A trend continues, however, to produce ever smaller particles for thick film applications. Generally, desirable features in such small particles include a small particle size; a narrow particle size distribution; a dense, spherical particle morphology; and a crystalline grain structure. Existing technology for manufacturing palladium-containing particles could, however, be improved with respect to attaining all, or substantially all, of these desired features for particles used in thick film applications. Improvements in the particles could result in significant performance advantages and/or cost savings when used to make electronic or other products.
One method that has been used to make small particles is to precipitate the particles from a liquid medium. Such liquid precipitation techniques are often difficult to control to produce particles with the desired characteristics. It is especially difficult by the liquid precipitation route to obtain particles having dense, spherical particle morphology and with good crystallinity.
Aerosol methods have also been used to make small palladium particles. One aerosol method for making small particles is spray pyrolysis, in which an aerosol spray is generated and then converted in a reactor to the desired particles. Spray pyrolysis systems involving palladium have, however, been mostly experimental, and unsuitable for commercial particle production. Furthermore, control of particle size distribution is a concern with spray pyrolysis. Also, spray pyrolysis systems are often inefficient in the use of carrier gasses that suspend and carry liquid droplets of the aerosol. This inefficiency is a major consideration for commercial applications of spray pyrolysis systems.
Additionally, palladium is easily oxidizable and has a tendency to oxidize during the manufacture of electronic devices. The oxidation of palladium during manufacture of electronic devices is problematic because volume expansion that accompanies oxidation can cause film cracking and delamination. It has been proposed that the susceptibility of palladium particles to oxidation is reduced by the addition of a small amount of an alkaline earth metal and by making the palladium particles as single-crystal particles to eliminate diffusion of oxygen along grain boundaries. Even with an alkaline earth additive, however, oxidation of palladium during the manufacture of microelectronic devices is still a significant problem and the cost of making single-crystal particles is high because of the high processing temperatures and long residence times required.
There is a need for improved palladium-containing powders, for improved methods of manufacturing palladium-containing powders and for improved products incorporating or made using improved palladium-containing powders.